1. Field of the Invention
The present invention relates to a technique to avoid illegal writing of data into a memory.
2. Description of the Background Art
In various services used are systems to download contents from servers via internet. In a service for downloading music data, for example, a user stores downloaded music data into his music player and then can enjoy playing the music. In another service, a user downloads a game program and stores it into his memory, and then can enjoy playing the latest game.
Such download services using a network are very useful in getting desired contents easily in a short time. This requires, however, some measures against illegal copy of contents.
Users can use such download services by storing downloaded contents into various storage media. In other words, an operation of writing contents into the storage media is performed by users in such services. This causes the possibility that the operation of writing contents might be observed. If it becomes possible for vicious people to freely perform such an operation, this may lead to illegal copy of contents. If no measure is done against such an illegal action, the authors of contents may be unduly robbed of their rights and profits.
For the purpose of protection against illegal copy of contents, for example, used is a technology called “CPRM (Content Protection for Recordable Media)”. “Copyright Protection Technology”, May 17, 2006, Japan Electronics and Information Technology Industries Association (JEITA), [queried on Jun. 15, 2006], at page 10 (hereinafter referred to as “Copyright Protection Technology”), discloses a system for copyright protection function, i.e., “CPRM”. A host equipment downloads a content with network encryption. Then, the host equipment creates an encryption key by using a device key of an equipment, a bunch of keys and a media ID of a memory card and the like and stores the content encrypted by using the encryption key into the memory card.
The technology disclosed in the above “Copyright Protection Technology”, i.e., “CPRM” and the like intend to avoid illegal use of contents by encryption of content data. In other words, this is an approach to prevent illegal use of contents by encryption of data itself written into storage media. Considering that illegal copy might become trickier in the future, it is desirable to develop a technology to prevent illegal copy from a new point of view.
Further, in the technology of “Copyright Protection Technology”, the contents with network encryption are once decoded by the host equipment. Therefore, since the decoded contents are temporarily stored in a RAM or the like inside the host equipment, there is a possibility that the state might be observed.